1. Field of the Invention
The present invention relates to a zoom lens ideal for digital still and motion cameras (DSMC), single-lens reflex cameras, and the like.
2. Description of the Related Art
Recently, in DSMCs and single-lens reflex cameras, zoom lenses are used in which a portion of the lenses in the first group are moved along the optical axis during focusing (see, for example, Japanese Patent Application Laid-Open Publication Nos. 2002-162564 and 2003-344766). Zoom lenses are also used in which a third or a fourth group configured by plural intermediate diameter lenses is moved along the optical axis during focusing (see, for example, Japanese Patent Application Laid-Open Publication No. 2010-44372).
For example, the zoom lens recited in Japanese Patent Application Laid-Open Publication No. 2002-162564 has, sequentially from an object side, a front lens component that includes plural lenses for performing zoom and focusing; and a rear lens component that includes a relay lens group having an imaging function. The rear lens component has, sequentially from the object side, a lens group A having a positive refractive power, a lens group B having a negative refractive power and movable so as to have a component in a direction orthogonal to the optical axis, and a lens group C having a positive refractive power, where the movement of the lens group B so as to have a component in a direction orthogonal to the optical axis causes displacement of the image.
The zoom lens recited in Japanese Patent Application Laid-Open Publication No. 2003-344766 includes, sequentially from the object side, a positive first lens group, a negative second lens group, a positive third lens group, and a positive fourth lens group, where the second lens group and the third lens group are moved in a direction along the optical axis to perform zooming. The first lens group is configured sequentially by a positive front group and a rear group having a stronger refractive power than the front group, where the rear group is moved in a direction along the optical axis to perform near focus and the front group is configured sequentially by a negative meniscus lens having a convex surface facing toward the object side, a positive lens whose object-side surface is convex, and a positive lens whose object-side surface is convex. The rear group is configured sequentially by a negative meniscus lens having a convex surface facing toward the object side, and a positive lens component.
The zoom lens recited in Japanese Patent Application Laid-Open Publication No. 2010-44372 has a first lens group having a positive refractive power and disposed farthest on the object side, a second lens group disposed on the image plane side of the first lens group, a Gn lens group disposed farthest on the image plane side, a Gn-1 lens group disposed on the object side of the Gn lens group, and at least 1 lens group disposed between the second lens group and the Gn-1 lens group. When zoom is performed, the first lens group and the Gn lens group are fixed. When focusing is performed, at least 1 lens group disposed between the second lens group and the Gn-1 lens group is moved and at least a portion of the Gn lens group is moved so as to have a component in a direction substantially orthogonal to the optical axis.
Nonetheless, the zoom lenses disclosed in Japanese Patent Application Laid-Open Publication Nos. 2002-162564 and 2003-344766 perform focusing by extending the first group that controls focusing and in which plural large diameter lenses are used. As a result, the first group is heavy and the effective diameter thereof is large, arising in problems of slow focusing speed and large power consumption by the drive apparatus driving the lens group.
Further, the zoom lens disclosed in Japanese Patent Application Laid-Open Publication No. 2010-44372 performs focusing by extending the third or the fourth group and although the third or the fourth group controlling focusing has an intermediate effective diameter, each is configured by intermediate diameter lenses and therefore, it is difficult to say that weight reduction is sufficiently facilitated. Consequently, if zoom and focusing are performed simultaneously, load is placed on the drive apparatus driving the lens group and it is difficult to perform quick zooming and focusing. Additionally, since this zoom lens has an absolute lateral magnification of 5 or less for the focusing group, the distance that the focusing group is extended for focusing from an infinity focus state to a near focus state becomes large, whereby the driving time for focusing increases and the quick capture of an image is difficult.